Zagros Fold Research Articles

The effects of plate margin inhomogeneity on the deformation pattern within west-Central Zagros Fold-and-Thrust Belt

Zagros Folded and thrust Belt (ZFTB) is a Cenozoic mountain belt in SSW of Iran and northeast of Arabia that resulted from closure of Neo-Tethys and collision between Arabia passive margin and Central Iran active margin. At this tectonic grain of Alp-Himalayan chain, change of the tectonic regime, degree of basement involvement, and character of accommodation of the deformation, in time and space, has been under debate. The results show that the deformation along the Zagros is not uniformly accommodated. Although the researchers have already paid attention to basement involvement in addition to the sedimentary cover rocks, little has been shown on the role of the basement's rigidity and lower crust's rheology on the deformation pattern along and across the belt. This study tries to address these questions in terms of inversion of slip vector of basement earthquakes, measurement of fault-slip data on the cover rocks, geomorphic and field observations, and existing geodetic and gravity data, with especial focus on Dezful embayment and surrounding area. The results show the Dezful embayment plays an indenter role. It, with the other reentrants, changes the obliquity of Arabian plate convergence, facilitates the escape of the upper crust toward free mechanical boundaries in salients, controls the slip-rate of Zagros Main Recent Fault at the rear of the belt and contributes in forming Zagros Fold-and-Thrust Belt as an orocline. The viscous lower crust helps the strain partitioning by providing a ductile shear base under the rigid upper crust.

Stratigraphic evidence for development of Aptian intrashelf basin in the Zagros area, eastern Fars Province, SW Iran

?The Lower Cretaceous of the Arabian Platform is renowned for the development of intrashelf basins. The study area is located in eastern Fars Province on the northeast Arabian plate and has experienced this environmental condition. The present study investigated two surface sections (Genau and Anguru) of the Dariyan Formation and compared the results with three neighboring wells in eastern Fars (eastern Zagros Fold Belt) in southern Iran to determine the development of rudist-bearing carbonates and intrashelf basin sediments. The Dariyan Formation was deposited in the Aptian as shallow-to-deep water carbonate facies. Lagoon, rudist banks/barriers, and open marine/basinal facies and six microfacies types have been distinguished. In the Genau section, the upper formation contains shallow rudistid limestone separated from the orbitolinid limestone of the lower formation by a deep pelagic unit. The pelagic sets disappear toward the Anguru section, but the rudistid unit remains. Abrupt changes were observed from shallow rudist facies to deep planktonic foraminifer facies. Comparison of the surface and subsurface sections (wells) suggests an intrashelf carbonate depositional model for the Dariyan Formation in the eastern Fars area. The term "Genau intrashelf" is proposed for this intrashelf basin surrounded by a shallow ramp. This intrashelf appears to be a northern subbasin of the Bab basin of the southern Persian Gulf. Extension of the Genau intrashelf subbasin and development of rudists around the margins of this intrashelf can be defined by tracing changes in the lateral facies of the Dariyan Formation.

Facies Changes Between Kolosh and Sinjar Formations Along Zagros Fold–Thrust Belt in Iraqi Kurdistan Region

The present study is concerned with lateral and vertical facies changes between Kolosh (Paleocene) and Sinjar (or Khurmala) (Paleocene-Early Eocene) Formations in Sulaimani and Duhok area, Kurdistan Region, NE-Iraq. The latter and former formations are belonging to basinal clastic (turbidite) and reefal carbonate facies respectively. The facies changes are documented in six sections by field studies and evaluation of previous ideas and data which are critically discussed and compared to the result of the present study. The special attention is directed towards the contact between the two Formations in relation to conformity. All the studies achieved before 2002 showed conformable contact between the two formations while the most recent study found large a gap (erosional unconformity) between the two formations which persisted for 5million years. According to latter study, the sea level fall associated with this unconformity assigned to be type one and type two sequence boundaries in the east of Darbandikhan, north of Koya towns and the Bekhme gorge.Conversely, the present study has not recorded gaps in the sedimentation in the studied sections either in Sulaimani or Dohuk area. The contact can be regarded as transgressive system tract which represented by green marl or sandstone, which changes to limestone of Sinjar or Khurmala Formation (HST).The conglomerate beds that are recorded in the previous studies at the contact of the two formations are not proved in the present study. The previously recorded conglomerate is located inside the upper part of the Kolosh Formation not in the contact and it represents submarine fan feeder channel. In contrast to previous studies, neither incised valleys nor erosional unconformity are found at the contact between the two formations in the studied area. The one meter intraformational conglomerate that are found (in some previous studies) in the Bekhme gore is not found in the present study. It is observed that the Kolosh Formation, at Bekhme Gore consists of green marl and sandstone with one bed of Khurmala Formation. The green marl is changes totally to dolomitic limestone of the latter Formation toward northwest at the north of Saru Kani village near Bujeel town. This proves that both formations are deposited in one basin and Khurmala formation has the age of Lower Paleocene to Lower Eocene.

Mineralogical and geochemical investigations of the Mombi bauxite deposit, Zagros Mountains, Iran

The Mombi bauxite deposit is located in 165km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE=162.8–755.28ppm, ave. ∼399.36ppm) relative to argillic limestone (ΣREE=76.26–84.03ppm, ave. ∼80.145ppm) and Sarvak Formation (ΣREE=40.15ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation.

Gas leakage hazard zonation of Masjed-i-Soleiman area, Zagros, Iran, using GiT

The shallow Masjed-i-Soleiman (MIS) oil field is situated at the Dezful Embayment in the Zagros Fold and Thrust Belt in southwestern Iran. The shallow depth of this oil field and multiple fractures has resulted in many gas leakages causing a significant pollution in residential areas around the area. In order to define the extent of the gas leakage, data sets such as surface structures, underground contour map, detected gas leakages, lithology, digital elevation models and population density were compiled using of remote sensing techniques and field investigations. The data were then added as layers in a geographic information system, which were overlaid form comparisons and used to construct a gas leakage hazard zonation map. This study shows that the central part of the MIS area, around the See-Berenj, Naftoon and Darre-Khersun districts, is a high-risk area, because of the shallow depth of gas caps, localizing of popular habitation and the high density of fractures and gas leakages.

Toward 4D modeling of orogenic belts: Example from the transpressive Zagros Fold Belt

Latest developments in computer power and computational solutions open new ways to envision complex natural systems. Advances in high-resolution 3D geodynamic modeling, in particular, allow investigating tectonic processes such as transpression, which involve “normal” and “tangential” kinematics with respect to the bulk orogenic trends. We demonstrate that implementing the 4 dimensions (space and time) provides and constrains new answers to long-lasting discussions. As case study, we have chosen the Zagros Simply Folded Belt in Iran, which exhibits spatial variations of structural patterns from the homogeneously shortened, wide fold belt in the Fars to the narrower, higher elevated area in the Izeh. High-resolution, 4D numerical modeling shows how a low-viscosity décollement becoming frictional toward the Dezful embayment influences the exposed fold patterns. Results also emphasize the importance of an oblique backstop to produce en-échelon arranged folds where convergence-related and backstop-controlled folds are mingled in the transpressional orogen.

ACTIVE DEFORMATION DELINEATED BY GEOMORPHIC AND SEDIMENTARY RESPONSE OF RIVERS, CENTRAL ZAGROS FOLD – THRUST BELT, SW IRAN

The mountain generation in Iran is because of continental collision between the Arabian and Eur-asia plate. Southwestern Iran shows active shorten that its evidences is deformation of crust and frequent earthquakes. At depth, active basement of the Zagros fold-thrust-belt in southwestern Iran, which are covered by folding of the Phanerozoic sediments, affected by some blind thrusted faults that have seismic nature. The Zagros fold-thrust-belt can be divided into 4 lithotectonic units including Sanandaj-Sirjan Zone (SSZ), Imbricate Zone (IZ), Zagros Fold Belt (ZFB), and Molasse Cover Sequence (MCS); this dividing and classification is based on geomorphology landscape, drainage pattern, rate of tectonics and stratigraphic records. Each tectonic unit characterized by especial abnormal forces in river systems. Active tectonics has the most important role to control the river systems by changing of channels incline. Change in the drainage pattern, channels cut, longitudinal profile, anomalous changes of sinuosity, changing of the side form and forming of terrace, change of river direction, compact meanders, cutting of meanders and geomorphology features of the rivers are responds to the active tectonics of region that are studied using remote sensing, DEM and field observations. These parameters are used to understand the vertical movement in the study area. Existing structures, especially growing anticlines and blind thrusted faults in the Zagros fold-thrust-belt, which cut the river channels and sometimes put them in parallel, are used in the study of their effect on the longitudinal and transverse tilt of morphological changes.

Lateral and depth variations of coda Q in the Zagros region of Iran

We have analyzed more than 2800 local earthquakes recorded by the Iranian National Seismic Network (INSN) and the Iranian Seismological Center (IRSC) to estimate coda wave quality factor, Q c , in the Zagros fold and thrust belt and the Sanandaj-Sirjan metamorphic zone in Iran. We used the single backscattering model to investigate lateral and depth variations of Q c in the study region. In the interior of Zagros, no strong lateral variation in attenuation parameters is observed. In SE Zagros (the Bandar-Abbas region) where transition to the Makran subduction setting begins, the medium shows lower attenuation. The average frequency relations for the SSZ, the Bandar-Abbas region, and the Zagros are Q c = (124 ± 11)f 0.82 ± 0.04, Q c = (109 ± 2)f 0.99 ± 0.01, and Q c = (85 ± 5)f 1.06 ± 0.03, respectively. To investigate the depth variation of Q c , 18 time windows between 5 and 90 s and at two epicentral distance ranges of R < 100 km and 100 < R < 200 km were considered. It was observed that with increasing coda lapse time, Q 0 (Q c at 1 Hz) and n (frequency dependence factor) show increasing and decreasing trends, respectively. Beneath the SSZ and at depths of about 50 to 80 km, there is a correlation between the reported low velocity medium and the observed sharp change in the trend of Q 0 and n curves. In comparison with results obtained in other regions of the Iranian plateau, the Zagros along with the Alborz Mountains in the north show highest attenuation of coda wave and strongest frequency dependence, an observation that reflects the intense seismicity and active faulting in these mountain ranges. We also observe a stronger depth dependence of attenuation in the Zagros and SSZ compared to central Iran, indicating a thicker lithosphere in the Zagros region than in central Iran.

Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

The isostatic modeling represents one of the most useful “geological” reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted “isostatic” Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub’ al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

Influence of surface processes and initial topography on lateral fold growth and fold linkage mode

Elongation of randomly distributed fold segments and their potential linkage are important for hydrocarbon exploration because it can greatly influence the morphology of the reservoir and both migration and accumulation of hydrocarbons in antiformal traps. Here we study the effects of surface processes and the presence of a topographic slope on the different linkage modes that can occur, and how these parameters affect the required horizontal offset for perturbations to link. The proposed numerical model represents a sedimentary cover detached over a much weaker basal decollement layer. The upper surface is modified by mass redistribution, which is achieved by a combination of fluvial and hillslope processes. Several series of simulations were performed: (1) without surface processes or regional slope, (2) with regional slope only, (3) with fluvial incision and hillslope processes, and (4) with hillslope processes only. Model results show that the presence of a regional slope reduces the critical distance required for the transition between linkage and no linkage modes, whereas erosion and redeposition of sediments, on the contrary, increase this distance. The location of the saddle point, where fold segments link, and its vertical distance to the crests of the anticlines are different compared to the case without erosion or initial topographic slope, which potentially can affect the morphology of hydrocarbon traps. Moreover, both erosion and redeposition of sediments enhance the fold elongation (growth along the fold axis), once the erosion velocity exceeds the folding velocity. Model results have been compared to the Zagros Fold Belt.

Geochemical characterisation, volumetric assessment and shale-oil/gas potential of the Middle Jurassic–Lower Cretaceous source rocks of NE Arabian Plate

ABSTRACT The Middle Jurassic–Lower Cretaceous strata of the NE Arabian Plate contain several prolific source rocks providing the charge to some of the largest world-class petroleum systems. They are located within the Zagros Fold Belt and Mesopotamian Foreland Basins covering the northern, central and southeastern parts of Iraq, Kuwait and western and southwestern Iran, particularly the Lurestan and Khuzestan provinces. These source rocks include the Bajocian–Bathonian Sargelu, the Callovian–Lower Kimmeridgian Naokelekan and the Upper Tithonian–Lower Berriasian Chia Gara formations of Iraq and their chronostratigraphic equivalents in Kuwait and Iran. They have charged the main Cretaceous and Cenozoic (Tertiary) reservoirs throughout Iraq, Kuwait and Iran with more than 250 billion barrels of proven recoverable hydrocarbons. These formations represent the transgressive system tracts of sequences deposited within deep basinal settings and anoxic environments. They are dominated by black shales and bituminous marly limestones, with high total organic carbon (TOC) contents (ranging from 1–18 wt%), and by marine Type IIS kerogen. Their Rock-Eval S2 yields may reach up to 60 mg HC/g Rock, particularly along the depocentre of the Mesopotamian Foreland Basin. The immature hydrogen index (HI) values might have been up to 700 mg HC/g TOC, whereas the present-day observed values vary depending on the location within the basin and the present-day maturity. The Source-Potential Index (SPI; i.e. mass of hydrocarbons in tons, which could be generated from an area of 1 sq m in case of 100% transformation ratio) averages around 2–3, but can even reach up to 14–16 along the basins’ centres. The Sargelu and the overlying Naokelekan-basinal Najmah formations (and their equivalents) could represent the best potential shale-gas/shale-oil plays in Iraq, Kuwait and Iran, due to their organic richness, favourable maturity and the presence of regional upper and lower seals. The estimated oil-in-place for the potential Sargelu shale-oil play in Iraq only is around 1,300–2,500 billion barrel oil-equivalent (BBOE) and in Kuwait is about 7–150 BBOE.

Age determinations of Cretaceous sequences based on calcareous nannofossils in Zagros Thrust and Folded Zone in Kurdistan Region-Iraq.

The studied area is located in Northern Iraq in the Kurdistan Region, in the North-&#x0D; Western part of the Zagros Fold belt. This study concentrates on the biostratigraphic&#x0D; approach using nannofossil analysis to identify the age of the formations that have&#x0D; deposited during Cretaceous period in Kurdistan Region-Iraq. The sedimentary&#x0D; sequences in Kurdistan region exhibit many lateral and vertical environmental and facies&#x0D; changes. Previously most of the works to recognize the age of the formations were&#x0D; concentrated on the Foraminifera zonation. In the present study, attempts have been&#x0D; made to review the age of the formations and the contact between them by using&#x0D; nannofossil analysis technique. Nannofossils assemblage Chia Gara Formations show&#x0D; that conformable contact situation between Jurassic-Cretaceous. The contact is between&#x0D; Late Tithonian Chia Gara and Berriasian- Valanginian Balambo formations. In Kurdistan&#x0D; during Hauterivian-Barremian the outer shelf sediment of Sarmord Formation deposited&#x0D; that conformably overlay Balambo Formation. The Qamchuqa Formation is a&#x0D; heterogeneous group of limestone. The lower part is belongs to the Aptian to Albian&#x0D; periods, while The upper part of the Qamchuqa limestone is generally dolomitized,&#x0D; therefore, the existed nannofossils even within the locally thin marl layers are destroyed.&#x0D; The Dokan Formation, which appears along the Dokan dam, is a Cenomanian age. The&#x0D; Kometan Formation is represented an Early Turonian age. The top of the Kometan&#x0D; limestone is characterized by a hard ground most possibly indicating a hiatus. The&#x0D; sequence of marl-Limestone of Shiranish Formation we dated Early to Late Campanian.&#x0D; Toward north the Early to Late Campanian part of Shiranish Formation can be locally&#x0D; replaced by the reefal Bekmeh limestone Formation. Very rare nannofossils were found&#x0D; in the marly intercalations of the Bekmeh limestone indicating at least a Late Cretaceous&#x0D; age. The Shiranish/Tanjero formations boundary lies within the Upper Campanian. The&#x0D; age of Tanjero Formation ranges from Late Campanian to Late Maastrichtian.

Kinematics and surface fracture pattern of the Anaran basement fault zone in NW of the Zagros fold–thrust belt

The preexisting north-south trending basement faults and their reactivation played an important role during the evolution of the Zagros fold-thrust belt. The Anaran basement fault in the Lurestan r ...

New Exploration Concepts in Zagros Fold Thrust Belt and Persian Gulf, Iran

Summary After more than 100 years hydrocarbon exploration, The Zagros Fold-Thrust Belt (ZFAB) is still remained as one of the most talented regions for future hydrocarbon discovery. Three main hydrocarbon structures originated from the Neogene folding, inherited deep-seated faults and buried salt diapirs. Remained many complex and small structures with potential prospect in the ZFTB which has not completely studied yet. They could be categorized in: (1) Fault related structures as subtle traps, which formed in response to intermediate detachments during Zagros folding or formed below the thrust faults, (2) Long time halokinesis prepared suitable small traps around the diapirs or under the salt sheets, (3) Inherited deep-seated fault movement and see-level changing formed stratigraphic-structural traps towards the palaeohighs, (4) Results of few drilled wells in pre-Permian sediments (Faraghan Formation) proved new gas reserves (5) and oil rings developed in some of onshore folded anticlinal. Consequently for future oil and gas exploration has to take two strategies. For oil exploration focuses more on the complex and small structures including subtle traps, stratigraphic-structural traps around salt diapirs and Palaeohighs. Whereas, for gas exploration remained many huge anticlines to the eastern part of ZFTB which has not been investigated in details.

Geochemical investigation, oil–oil and oil–source rock correlation in the Dezful Embayment, Marun Oilfield, Zagros, Iran

Geochemical analysis of crude oils from Bangestan and Khami reservoirs, and potential source and reservoirs rocks from the Marun Field in the Dezful Embayment, Zagros Fold Belt Iran show that the Kazhdumi Formation (Fm.) is likely to be thermally mature (at least in the oil window) across the entirety of the Marun field, and that it has excellent generative potential as a source rock. Geochemical data also suggest the Pabdeh Formation has remarkable generative potential but is not thermally mature at the crest of the Marun field, although it is likely to be thermally mature in synclinal regions to the NE and SW. The Gurpi Formation, while thermally mature (early oil window) has marginal generative potential. It is notable, therefore, that oils from the Bangestan and Khami reservoirs have biomarker characteristics that do not match bitumen obtained from the Kazhdumi Formation. Examples of this include the ratio of diasteranes to steranes, the proportions of different carbon numbered hopane homologues and the ubiquitous occurrence of alkylated-trimethyl-benzenes. These biomarker characteristics could only have been imparted to the Bangestan and Khami oils by a source rock other than the Kazhdumi Formation. This contrasts with the stable isotope composition of the Bangestan and Khami oils which suggest correlation to the Kazhdumi Formation. Biomarkers are a quantitatively minor fraction of oil, thus it is possible that the biomarker characteristics of the oils was created by mixing Kazhdumi-bitumen with other petroleum from the Gurpi and Pabdeh formations. This could happen if 1) multiple oil charges from different source kitchens filled the same reservoir, or 2) if oil migrated vertically from the flanks and crossed the Gurpi and Pabdeh formations – both of which have been considered regional seals. Both scenario 1) or 2) would point to a filling history more complicated than previously conceived.

Geological analysis and updating velocity model by restoration of a cross section in Zagros fold–thrust belt in the southwest of Iran

The Zagros region (SW Iran) contains dominant parts of the remaining Iranian natural resources. Covering Abadan Plain, Dezful Embayment, and Izeh zone, this paper studies a structural cross section constructed across the Zagros belt using 2D and 3D seismic data, well data, surface and subsurface geological maps, satellite images, and field reconnaissance. Restoration assists us for validation and modification of the constructed cross section, better understanding of geology and stratigraphy of the Zagros basin, and computing an updated velocity model in seismic time to depth conversion. In the area of interest, Hormuz basal decollement and Gachsaran detachment play the most significant role in structural style and deformation of the Zagros. More complication links with interval decollements such as Triassic evaporites, Albian shales, and Eocene marls. Estimation of shortening is complex because of a variety of lithotectonic units and detachment surfaces. Here, we are about to introduce a new approach to update seismic velocity model by means of deduced balanced depth model by restoration and seismic two-way time. This is valuable in the case of thick sedimentary cover and steep dip of faults, where acquired seismic images are ambiguous and unreliable. The seismic velocity of Asmari and Gachsaran formations mainly depends on lateral facies and thickness variations within the overburden sediments and generally increases across the Zagros belt from foreland towards hinterland.

Geologic evolution of the Iraqi Zagros, and its influence on the distribution of hydrocarbons in the Kurdistan region

Whereas the vast majority of discovered hydrocarbon reserves in Iraq reside in Cretaceous and Cenozoic reservoirs, numerous oil and gas fields have been discovered recently in deeper Jurassic and Triassic reservoirs in the Kurdistan region of Iraq. This study presents a Middle–Upper Jurassic thermal maturity map for the Kurdistan region of Iraq and demonstrates that regional first-order trends in Jurassic source rock maturity show a close correlation to the spatial distribution of oil gravities within the overlying Jurassic (and Cretaceous) reservoirs. This distribution is consistent with compartmentalization of the active source rock kitchens due to Zagros folding, resulting in relatively short-distance migration and charge of the anticlinal structures from the adjacent synclinal lows. The thermal maturity map confirms relatively low maturity over the Mosul high, where the Cretaceous and Cenozoic section overlying the source rock interval is relatively thin, and increasing maturity to the southeast as the thickness of the Cenozoic foredeep sediments increases toward the depocenter located in the southeastern Iraqi Zagros and the adjacent Iranian Zagros. The correlative trend in oil gravities is exemplified by the recent Jurassic discoveries: low to medium gravity oils (14–27° API) in Shaikan and Atrush to the northwest, light oil (39–47° API) in Mirawa and Bina Bawi, and gas condensate (55° API) in Miran West to the southeast. Understanding thermal maturity patterns and hydrocarbon fluid-type distributions will help to guide risk assessment for remaining prospectivity and future exploration drilling within the Kurdistan region of Iraq.

Tectonic Geomorphology of Iran’s Salt Structures

Iran has a various salt structures that their tectonic geomorphology is subject of this paper. Geologic situation of salt structures in Iran have determinate. According to age and geological setting of salt deposits that revealed by tectonic geomorphology methods, salt structure provinces of the Central and Southern Iran have been distinguished. Also, critical concepts of salt diapirism in the Southern Iran and Central Iran salt basins have explained. Therefore, Central Iran’s salt diapirs have triggered by tectonic forces, but salt diapirism in the Southern Iran has triggered by halokinesis, then it has effected by tectonic forces, especially in Zagros fold and thrust belt.

Analysis of natural fractures and effect of deformation intensity on fracture density in Garau formation for shale gas development within two anticlines of Zagros fold and thrust belt, Iran

Abstract Shale-gas production depends on natural and hydraulic fractures to flow it to well. A major part of source rocks in the Zagros Fold Belt was deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan subzone, which has a potential of being as a shale-gas resource. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the Dezful Embayment. Knowing factors which control fracture intensity and fracture length in each area are important in drilling into shale-gas resources. In this regard, a very dense and accurate field data acquisition on fracture sets, orientation, length, as well as bedding thickness, texture and lithology was carried out in Early Cretaceous Garau Formation and basal Sarvak Formation within two anticlines with different structural settings (Kabir-Kuh and Khoram-Abad). According to our analyses, we have identified 2 fracture systems: (1) an orthogonal fracture system: set A in Khoram-Abad anticline and sets A and B in the Kabir-Kuh anticline and a longitudinal fracture set: set B in Khoram-Abad anticline and sets C and D in the Kabir-Kuh anticline, (2) an oblique fracture system: sets C and D in Khoram-Abad anticline and set E in the Kabir-Kuh anticline. The normal faults and stylolites (prior to stylolitization) in the study area of Kabir-Kuh anticline had formed in response to extension stress regime and the transverse fractures in the study area of Khoram-Abad anticline are Early Cretaceous to Late Oligocene in age, then the transverse fractures and their orthogonal stylolites in Kabir-Kuh anticline and longitudinal and oblique fracture systems in the Khoram-Abad anticline have formed from Early Miocene to Middle Late Miocene, while longitudinal and oblique fracture sets in the Kabir-Kuh anticline have formed since Middle Late Miocene. We suggest that there have been two phases of counterclockwise rotations in orientation of the stress fields that had produced these fractures. The rotations in the stress field have probably occurred due to rotation of the Arabian plate during its convergence to the Eurasian plate which had changed the orientation of fractures. These rotations forming some range of fractures with different attitudes, that now with recent direction of impression apply by the Arabian plate those fractures which generate in the past would have shown different reaction. In our study area in addition to transverse fracture sets which originated near parallel to maximum horizontal stress, one set of oblique fractures is the second normal fracture set which is reactivated in response to fluid pressures, prior to origination of new hydraulic fractures. In the Lurestan structural province, deformation intensity is increased from the Kabir-Kuh anticline in the southern part of the Lurestan structural province to the Khoram-Abad anticline in the northeastern part of the province. In the Kabir-Kuh anticline, lithology has played the most important role in fracture intensity, so that in some places even with increasing bedding thickness, we observe an increase in fracture intensity instead of the expected decreasing fracture intensity. While in Khoram-Abad anticline bedding thickness has the most important effect on fracture intensity, and lithology has a minor role. In both investigated areas, fracture length is increased with changing texture from mudstone to wackstone and also from wackstone to packstone.

The Khersan 3 Archaeological Survey: New Insights into Settlement Patterns in the Zagros Folding Zone from Hydro-Dam Project Archaeology

The Khersan 3 Archaeological Survey: New Insights into Settlement Patterns in the Zagros Folding Zone from Hydro-Dam Project Archaeology